The present invention relates to a new and improved method of, and apparatus for, bending a strand in a continuous casting installation, especially for casting steel strands.
Generally speaking, the invention contemplates supporting the ferrostatic pressure of a continuously cast strand having a liquid core or sump at a transition curve along a bending path between a circular arcuate-shaped roller apron track and a linear roller apron track by means of pairs of support rolls.
During the bending of continuously cast strands in continuous casting installations for steel, it is already known in this technology, for instance from German Patent Publication No. 2,341,563 and the corresponding U.S. Pat. No. 3,893,503, granted July 8, 1975, both during bending of a straight strand along a circular arc and also during the straightening of a curved strand, to accomplish the bending work in a number of successive steps, so that the strand is less intensely loaded at the bending region or zone in contrast to a single-point bending or single-point straightening, as the case may be. During the stepwise bending operation the bending radius is therefore stepwise or incrementally reduced and/or during the stepwise straightening operation such bending radius is stepwise or incrementally increased. When designing a continuous casting installation for casting strands working with an arc-type or curved continuous casting mold having a relatively small radius and with a subsequently arranged circular arcuate-shaped roller apron or strand supporting and guide arrangement as well as a stepwise straightening operation, there can be obtained a low structural height of the installation and, in actual practice, tolerable elongation values at the strand shell or skin in the straightening section of the roller apron. However, the alignment of such roller aprons or strand supporting and guiding arrangements is extremely complicated because, on the one hand, the rolls or rollers of both support tracks must be exactly aligned along the bending path and, on the other hand, the bending path must be exactly aligned with respect to the curved roller apron track and the straight roller apron track.
Furthermore, there is known to the art, for instance as exemplified by U.S. Pat. No. 3,324,931, granted June 13, 1967, a roller apron or strand supporting and guide arrangement for supporting and guiding as well as for deflecting or turning an only partially solidified cast strand. With this roller apron at the roll pair bounding the bending path of a straight and a curved part of the roller apron one of the rolls is fixedly arranged. Along the bending path there are arranged roll pairs for supporting the ferrostatic pressure, and at least four of such rolls are rigidly connected to form force-transmitting bending or straightening rolls, as the case may be, and of which two are provided at the side of the strand where the fibers undergo tensile forces and at least two are provided at the side of the strand where the fibers experience compressive forces. Also with this bending apparatus the exact alignment of the rolls along the transition curve and in relation to the circular arcuate-shaped roller apron track and the straight roller apron track is difficult and time-consuming. During bending of the continuously cast strand, the elongation velocity or speed at the solidification front alters in a stepwise or incremental fashion along the bending path from null up to a maximum value and again then in stepwise fashion back to null. This bending characteristic increases the total bending path by the ascending and the descending portion of the elongation velocity change along the bending path. In order to obtain small elongation velocity values along a bending path between a straight continuous casting mold and a circular arcuate-shaped roller apron section, it is therefore necessary to provide a corresponding length for such bending path with a corresponding structural height of the continuous casting installation, something negatively affecting the costs of the continuous casting installation. The alignment work which must be accomplished at such bending path poses high demands and requirements and is complicated and time-consuming to carry out.